For devices used in interventional cardiology and peripheral vascular procedures, such as a therapeutic or diagnostic medical device intravascular catheter, one of the most important design considerations is minimizing the outer diameter of such devices in order to facilitate delivery into vessels with decreasing vessel lumen diameter. This outer diameter is often referred to as the device “profile”. These intravascular catheters frequently incorporate therapeutic devices at the distal end, such as inflatable balloons, expandable vascular stents or embolic protection devices (EPD) such as filters, and it is critical to design catheters which can accommodate these therapeutic devices in a radially collapsed, crimped or otherwise radially constrained configuration, while maintaining an acceptably “low-profile” delivery configuration.
Once these intravascular catheters have been introduced and the distal end of the catheter is properly positioned at the desired treatment site, the collapsed therapeutic device is released from its crimped or constrained condition, and permitted to expand to a larger diameter for the therapeutic purpose. Therapeutic devices deployed at the distal end of such interventional catheters often comprise self-expanding stent or EPD systems, which are constructed of various shape-memory alloys (e.g., nitinol) that expand into contact with the vessel wall upon release from the catheter due to their shape-memory properties.
Nitinol-based devices, such as an EPD, would typically be crimped or radially-collapsed into a low-profile diameter during the process of loading into the distal end of the catheter, and would be constrained in this collapsed configuration during introduction and delivery through the related vasculature. For catheter based delivery systems, this constraint is accomplished by use of a constraining sheath which overlies the collapsed therapeutic device loaded in the distal end of the delivery catheter. The therapeutic device is typically delivered to the vascular treatment site by relative longitudinal movement between the EPD and constraining sheath. This relative longitudinal movement, for example, is accomplished by either slidably retracting the constraining sheath to release a stationary EPD, or alternatively by pushing a moveable EPD out the distal end of a stationary constraining sheath, thereby deploying the self-expanding EPD into vessel wall apposition within the vessel lumen being treated.
When loading the EPD into the constraining sheath, the tendency for the loaded EPD to self-expand against the interior surface of the constraining sheath will generate sufficient frictional forces which help to stabilize the EPD in its loaded position at the distal of the catheter during navigation and delivery to the treatment site. However, the process of deploying the EPD into the vessel necessarily requires overcoming these frictional forces in order to release the self-expanding EPD by either proximally retracting a moveable constraining sheath, or by distally advancing a EPD out from the distal end of a stationary constraining sheath. These frictional forces generally increase as a function of collapsing the EPD into the smallest possible device profile for delivery and deployment.
Since the EPD is loaded at the distal end of the catheter, and in vivo deployment of the EPD is at a vascular location quite remote from the proximal end of the catheter being manipulated by the interventional vascular practitioner, virtually all of the forces applied to the EPD and constraining sheath must be transferred through the entire length of the delivery catheter to accomplish the deployment process. In the case of an EPD mounted to an independent, pre-deployed guidewire, for example, it may be very difficult to accomplish deployment, since the column strength of the guidewire at the tapered end where the EPD is attached will be very limited.
Thus, it would be desirable to provide an EPD delivery catheter having a constraining sheath design adapted for release of the constrained EPD in a manner which significantly minimizes the problem of force transfer. Since most of the forces exerted between the EPD and constraining sheath during deployment relate to overcoming friction associated with relative longitudinal movement between the sheath and constrained EPD, it would be desirable to provide a delivery catheter and method for release of the EPD from a constraining sheath which greatly reduces or eliminates these frictional forces. Furthermore, it would be desirable to provide an EPD delivery catheter and method that would allow simple EPD from a very low profile catheter.
The delivery tubes and methods of the present disclosure solve one or more of the problems set forth above.